Anisotropy in Bi ₂ Sr ₂ CaCu ₂ O _{8+ <i>x</i>} Films at Microwave Frequencies: Enhancement of Dissipation in Parallel Magnetic Field

Abstract

Magneto-resistive measurements at microwave frequencies have been carried out in c-oriented Bi2Sr2CaCu2O8+x films. When the angle curly theta between the magnetic-field direction and the (a, b)-plane is varied a large anisotropy is observed in the microwave absorption. In the range 4-degrees < curly theta less-than-or-equal-to 90-degrees, the dissipation scales as H sin curly theta, but below 4-degrees an anomalous enhancement of dissipation is present. The behaviour of the enhancement is measured as a function of the temperature in the range (70 divided-by 85) K.